This utility parses an Apache log file and determines how many unique domains visited your site, then compiles a list of them (good for directing to an email or logfile).
It uses a cache file to speed up the process as well (not having to do DNS lookups all the time). It only handles the first level of a domain, IE: blah.mchsi.com and dink.mchsi.com will just be listed as 2 entries from mchsi.com.